Liquid crystal display device having uniform integrated spacers

ABSTRACT

A reflective liquid crystal display (LCD) device includes a plurality of openings patterned in the pixel metal layer in the peripheral region of the device exposing the insulating layer beneath, a plurality of light-shielding islands beneath the openings in the pixel metal layer, and a plurality of walls formed on the islands surrounding the openings and extending substantially between the islands and the pixel metal layer. A plurality of spacers are disposed on the exposed portions of the insulating layer in the peripheral region for supporting the transparent (e.g., glass) layer above and providing a space for the liquid crystal material. The structure enhances display uniformity by making the spacers formed in the peripheral area more closely match the spacers formed in the pixel area of the device. The structure also prevents light from reaching the substrate in the peripheral region of the device and permits portions of the second metal layer formed in the peripheral region of the device to be used for signal routing.

This is a divisional of application Ser. No. 09/833,718, filed Apr. 13,2001, now U.S. Pat. No. 6,642,986.

BACKGROUND OF THE INVENTION

1) Field of the Invention

This invention pertains to the field of liquid crystal display (LCD)devices, such as liquid crystal on silicon (LCOS) devices, and moreparticularly to a structure for such a device providing for uniformspacers.

2) Description of the Related Art

Reflective LCD devices are well known. Examples of such devices, and inparticular active matrix devices, are shown in U.S. Pat. Nos. 6,023,309and 6,052,165. With reference to the following description, familiaritywith conventional features of such devices will be assumed, so that onlyfeatures bearing on the present invention will be described.

FIG. 1 shows a portion of a typical prior-art reflective LCD device 100.The reflective LCD device 100 may generally be divided into a pixelregion 100 a (active region) and a peripheral region 100 b. The pixelregion 100 a includes an array of pixel elements and the peripheralregion 100 b includes driver circuits 105 for supplying driving signalsto each of the pixel elements.

The LCD device 100 comprises, in relevant part, a silicon substrate 110,an insulating layer 112, a liquid crystal layer 114 a transparentelectrode 116, such as indium-tin-oxide (ITO), and a transparent (e.g.,glass) layer 118. A reflective mirror (pixel) metal layer 120 isprovided beneath the liquid crystal layer 114 on the insulating layer112. The mirror metal layer 120 includes a plurality of individualreflective pixel electrodes 120 a in the pixel region 100 a, and asubstantially continuous peripheral portion 120 b formed in theperipheral region 100 b of the LCD device 200. Light transmissiveregions 122 are located between the pixel electrodes 120 a.

Also provided in the insulating layer 112 and between the mirror metallayer 120 and the substrate 110 are a light shield metal layer 124 androuting metal layers, 128 and 130. In the pixel region 100 a, the metallayers 128 and 130 form mutually-orthogonal row and column lines, whichmay be connected to gate and source electrodes of MOS transistors (notshown in FIG. 1) for pixel elements fabricated in the underlyingsubstrate 110. In the peripheral region 100 b, the metal layers 128 and130 form signal routing lines used for routing various signals of thedriver circuits. Also, metal plugs or vias 132 are provided forconnecting various portions of the light shield metal layer 124 and thethird and fourth metal layers 128, 130 with each other.

The metal layer 124 is provided to prevent light entering the device,such as through the transmissive regions 122 between the pixelelectrodes 120 a, from reaching the substrate 110 where it might induceleakage currents on otherwise interfere with proper device operation.While portions of metal layers 128 or 130 may incidentally block a smallportion of light entering the device, the structure of FIG. 1 requires aseparate metal layer 124 to be dedicated to provide the required degreeof light blocking in the peripheral region 100 b.

A plurality of spacers or pillars are provided for supporting thetransparent layer 118 and providing a gap for the liquid crystal layer114. In the pixel region 100 a, the spacers 134 a are placed directly onthe insulating layer 112. In the peripheral region 100 b, spacers 134 bare provided on the peripheral portion 120 b of the mirror metal layer120.

In order to maintain a uniform liquid crystal cell gap, it becomesnecessary for the spacers in the peripheral region 100 b to have aheight that is the same as the spacers in the pixel region 100 a.However, the spacers 134 b formed on the mirror metal layer 120 in theperipheral region 100 b are taller than the spacers 134 a formed on theinsulating layer 112 in the pixel region 100 a because of the extraheight of the metal layer 120, thus producing a non-uniform display.

Accordingly, it would be desirable to provide a liquid crystal displaydevice having spacers with a more uniform height in both the pixel andperipheral regions of a reflective LCD device. Other and further objectsand advantages will appear hereinafter.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a liquid crystaldisplay (LCD) device having a more uniform spacer structure.

In accordance with one aspect of the invention, an LCD device isprovided having a pixel region and a peripheral region adjacent to thepixel region, comprising a silicon substrate, an insulating layer on thesubstrate, a first metal layer above the insulating layer including anarray of pixel electrodes in the pixel region and a peripheral portionin the peripheral region having a plurality of openings therein, aplurality of spacers in the openings, a second metal layer between thefirst metal layer and the substrate, and a plurality of walls eachcorresponding to one of the plurality of openings and extendingsubstantially between the second metal layer and the first metal layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a simplified cross-sectional view of a portion of aprior-art liquid crystal display (LCD) device;

FIG. 2 shows a simplified cross-sectional view of a portion of oneembodiment of an LCD device having integrated spacers in accordance withone or more aspects of the invention; and

FIG. 3 shows a top plan view of a portion of the LCD device shown inFIG. 2.

DETAILED DESCRIPTION

FIG. 2 shows a simplified cross-sectional view of a portion of areflective LCD device 200 in accordance with one or more aspects of theinvention. For clarity, those portions of the device relating to thepresent invention are illustrated. The reflective LCD device 200 maygenerally be divided into a pixel region 200 a (active region) and aperipheral region 200 b. The pixel region 200 a includes an array ofpixel elements, and the peripheral region 200 b includes driver circuits(not shown in FIG. 2) for supplying driving signals to each of the pixelelements.

The LCD device 200 comprises, in relevant part, a silicon substrate 210on which are successively provided an insulating layer 212, a liquidcrystal layer 214, a transparent electrode 216, such as indium-tin-oxide(ITO), and a transparent (e.g., glass) layer 218. A first metal layer220 is provided on the insulating layer 212 beneath the liquid crystallayer 214. The first metal layer 220 includes a plurality of individualreflective pixel electrodes 220 a formed in the pixel region 200 a, anda peripheral portion 220 b formed in the peripheral region 200 b of theLCD device 200. Light transmissive regions 222 are located between thepixel electrodes 220 a. A plurality of openings 220 c are formed in theperipheral portion 220 b of the first metal layer 220, each openingexposing a portion of the insulating layer 212.

Also, a second metal layer 224 is provided between the first metal layer220 and the substrate 210. The second metal layer 224 includes a lightshield portion 224 a in the pixel region 200 a, and a plurality ofsignal routing lines 224 b and light shields 224 c in the peripheralregion 200 b. At each of the light shields 224 c is provided alight-blocking partition or wall 226 extending substantially between thelight shield 224 c and the peripheral portion 220 b of the first metallayer 220. Third and fourth metal layers 228 and 230 are providedbetween the second metal layer 224 and the substrate 210. Also, metalplugs or vias 232 are provided for connecting various portions of thesecond, third, and fourth metal layers with each other.

A plurality of integrated spacers or pillars 234 are provided forsupporting the transparent electrode 216 and transparent layer 218 andproviding a gap for the liquid crystal layer 214. In the pixel region200 a, the spacers 234 are placed directly on the insulating layer 212in the light transmissive regions 222 between the pixel electrodes 220a. In the peripheral region, the spacers 234 are located on the openings220 c in the peripheral portion 220 b of the first metal layer 220.Preferably, the spacers 234 may be formed by uniformly applying acoating (e.g., Si₃N₄; SiO₂) over the first metal layer 220 and exposedinsulating layer 212 to a desired height, and etching the coatedmaterial to produce the spacers 234. The height and diameter of thespacers 234 are selected to provide the desired gap for the liquidcrystal layer 214, and the required strength to support the transparentlayer 218. In one embodiment, the spacers 234 may have a height of 1-2μm, and as small a diameter as 0.4 μm. Larger spacers, which simply themanufacturing process, may also be employed.

An operation of various pertinent elements of the embodiment will now bedescribed.

Beneficially, the first metal layer 220 is a mirror (pixel) metal layer,such that it blocks light which directly impinges on it from reachingthe substrate 210. However, openings 220 c are produced in theperipheral portion 220 b of the first metal layer 220 in the peripheralregion 200 b so that the spacers 234 in the peripheral region 200 b maybe of a uniform height with the spacers 234 in the pixel region 200 a.Accordingly, it is necessary to prevent light which impinges on theopenings 220 c from reaching the substrate 210.

For this purpose, it is possible to use the second metal layer 224 as asubstantially continuous dedicated light shielding area covering theentire peripheral region 220 b. In that case, any light which would passthrough the openings 220 c in the first metal layer 220 would be blockedby the second metal layer 224 from reaching the substrate 210 in theperipheral region 200 b.

However, the area required for the driver circuits 205 can be reduced ifthe metal layer 224 could also be used for routing driver circuitrysignals in the peripheral region 200 b, instead of being dedicated onlyto light blocking.

Accordingly, in the preferred embodiment, the second metal layer 224includes the light shields 224 c in the peripheral region 200 b arrangedbeneath each of the openings 220 c. Preferably, each light shield 224 cis an island, substantially disconnected from a remainder of the secondmetal layer 224. Additionally, on each of the light shields 224 c isprovided the light-blocking partition or wall 226 extendingsubstantially between the light shield 224 c and the peripheral portion220 b of the first metal layer 220. Preferably, the wall 226 iscontinuously formed around the entire opening 220 c. Also, preferably,the wall 226 extends vertically to connect the light shield 224 c to theperipheral portion 220 b of the first metal layer 220.

FIG. 3 shows a top plan view of a portion of the peripheral region 200 bof the LCD device 200 in the vicinity of one of the openings 220 c inthe first metal layer 220. As shown in FIG. 3, in one embodiment theopening 220 c in the peripheral portion 220 b of the first metal layer220 is in the shape of a cross, and the spacer 234 is located in themiddle of the intersection of the cross. In one embodiment, theend-to-end length of the “cross” in each of the “x” and “y” directionsis 1.2 μm. This mimics the area between pixel electrodes 220 a where thespacers 234 are located in the pixel region 200 a, producing betterdisplay uniformity.

Meanwhile, the light shield 224 c is an island that may be of anyconvenient size or shape, so long as it is at least as large as theopening 220 c. In one embodiment, the length of the light shield in eachof the “x” and “y” directions is 3.5 μm. The wall 226 may also be of anyconvenient size or shape, so long as it substantially encloses theopening 220 c, and is no larger than the light shield 224 c.

Preferably, the wall 226 is formed by patterning a vertically-extendingvia in the insulating layer 212 and depositing a light-blocking materialtherein prior to depositing the first metal layer 220. The wall 226 maybe formed in a same step as the formation of the metal plugs 232connected to the pixel electrodes 220 a. Also, preferably, the wall 226is formed of Tungsten. In this case, the wall 226 is formed of the samematerial as the vias 232 in the insulating layer 212, thus requiring noadditional processing steps. However, other light blocking materials andmethods of fabrication may be used. In one embodiment, the wall 226 hasa height of approximately 1 μm so as to extend vertically between andconnect the first metal layer 220 and the second metal layer 224. Inthat case, the thickness of the wall 226 may be approximately 0.4 μm.

While the present invention has been particularly shown and describedwith reference to the preferred embodiments thereof, it will beunderstood by those skilled in the art that various changes in detailmay be made without departing from the scope of the invention as definedby the claims.

What is claimed is:
 1. A method of producing a liquid crystal display(LCD) device having a pixel region and a peripheral region adjacent tothe pixel region, comprising: forming an insulating layer on asubstrate; forming a first metal layer above the substrate; forming apixel metal layer above the first metal layer, the pixel metal layercomprising an array of pixel electrodes in the pixel region, and aperipheral portion in the peripheral region having a plurality ofopenings therein exposing portions of the insulating layer; and forminga plurality of walls, each corresponding to a corresponding one of theplurality of openings and extending substantially between the firstmetal layer and the peripheral portion of the pixel metal layer.
 2. Themethod of claim 1, wherein forming the first metal layer comprises:forming a plurality of light shields directly beneath the openings inthe peripheral portion of the pixel metal layer, and forming a pluralityof signal routing lines in the peripheral region.
 3. The method of claim1, wherein each wall is formed substantially continuously around thecorresponding opening.
 4. The method of claim 1, wherein the wall isformed of an opaque material.